Re: [net-next 11/13] igb: Make Tx budget for NAPI user adjustable

Ben Hutchings
2011-09-19T16:05:55Z

On Mon, 2011-09-19 at 08:48 -0700, Alexander Duyck wrote:
> On 09/17/2011 10:04 AM, Ben Hutchings wrote:
> > On Sat, 2011-09-17 at 01:04 -0700, Jeff Kirsher wrote:
> >> From: Alexander Duyck<alexander.h.duyck@intel.com>
> >>
> >> This change is meant to make the NAPI budget limits for transmit
> >> adjustable. By doing this it is possible to tune the value for optimal
> >> performance with applications such as routing.
> > [...]
> >> --- a/drivers/net/ethernet/intel/igb/igb_ethtool.c
> >> +++ b/drivers/net/ethernet/intel/igb/igb_ethtool.c
> >> @@ -1989,6 +1989,9 @@ static int igb_set_coalesce(struct net_device *netdev,
> >> if ((adapter->flags& IGB_FLAG_QUEUE_PAIRS)&& ec->tx_coalesce_usecs)
> >> return -EINVAL;
> >>
> >> + if (ec->tx_max_coalesced_frames_irq)
> >> + adapter->tx_work_limit = ec->tx_max_coalesced_frames_irq;
> >> +
> > [...]
> >
> > I don't think it really makes sense to conflate NAPI and interrupt
> > moderation parameters. This really ought to be added to NAPI itself.
> >
> > (NAPI contexts really ought to be exposed through sysfs somehow. I
> > think we've discussed this before, and it's tricky due to the lack of a
> > consistent mapping between those contexts and net devices.)
> >
> > Ben.
>
> All NAPI does is move things from a hard interrupt to a soft interrupt
> in the case of TX cleanup. If it wasn't for NAPI we would be calling
> ixgbe_clean_tx_irq directly from the interrupt handler and would still
> be using the same limiting value. This is why placing it here makes sense.

But tx_max_coalesced_frames_irq is not supposed to be a work limit (and
such a work limit doesn't seem useful in the absence of NAPI). As I
understand it, it is supposed to be an alternate moderation value for
the hardware to use if a frame is sent while the IRQ handler is running.

Ben.

--
Ben Hutchings, Staff Engineer, Solarflare
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